1. Field of the Invention
This invention relates to an in-vehicle engine control device which rapidly excites an electromagnetic coil for driving a solenoid valve by using a boosting circuit unit which generates a high voltage from an in-vehicle battery and then performs valve-opening holding control by using a voltage of the in-vehicle battery, in order to drive the solenoid valve for fuel injection of an internal combustion engine at high speed, and particularly to an in-vehicle engine control device including an improved boosting circuit unit for obtaining a boosted high voltage and a control method thereof.
2. Description of the Background Art
There is an in-vehicle engine control device which sequentially generates valve opening command signals to a plurality of electromagnetic coils which are respectively provided for cylinders of a multi-cylinder engine and drive a fuel injection solenoid valve by using a microprocessor which is operated according to a crank angle sensor, so as to sequentially selectively set valve opening time and valve opening period, and performs rapid excitation control and valve opening holding control by using an solenoid valve driving control circuit unit so as to perform rapid valve opening and valve opening holding of the solenoid valve. In this in-vehicle engine control device, it is well known that a value of a boosted high voltage generated by the boosting circuit unit which determines a high-speed valve opening performance of the solenoid valve is variably adjusted according to a fuel pressure, a value of an intermittently driven current for an inductive element provided in the boosting circuit unit is variably adjusted according to engine speed or a battery voltage, an output voltage of the boosting circuit unit is automatically adjusted such that an actual voltage applied to the electromagnetic coil becomes a predetermined high voltage, or a boosted high voltage is automatically adjusted such that a peak current which flows through the electromagnetic coil becomes a predetermined target current. In these well-known examples, targeted rapid excitation control and valve-opening holding control are performed by detecting an excitation current for the fuel injection electromagnetic coil, detecting a boosted voltage of the boosting circuit unit, or detecting a driving current of the boosting inductive element.
For example, according to FIG. 1 of PTL 1, entitled “fuel injection valve control device”, a microcomputer 12 detects a peak current Ip which flows through fuel injection electromagnetic solenoids INJ1 and INJn during a rapid excitation period by using a current detection resistor R10, adjusts a conduction duty cycle of a MOS transistor MN1 depending on a difference from a target peak current Ip0, and charges a capacitor C1 by intermitting a current of a boosting inductor L1 (boosting inductive element). In addition, the microcomputer 12 monitors a divided voltage V1 of a voltage across both ends of the capacitor C1, and adjusts a conduction duty cycle such that a predetermined target voltage for obtaining the targeted peak current Ip0) can be obtained. Thereby, it is possible to reliably perform appropriate fuel injection at engine speed from a low speed zone to a high speed zone. In this example, an excitation current of the electromagnetic solenoid (electromagnetic coil) is detected using the current detection resistor so as to be input to the microcomputer, and a boosted high voltage is divided by a dividing resistor so as to be input to the microcomputer, but a driving current for the boosting inductive element is not detected.
In addition, according to FIG. 1 of PTL 2, entitled “boosting power supply device”, in a circuit in which a coil 2 to which a power supply voltage VB is supplied, a transistor 3, and a current detection resistor 4 are connected in series, a series circuit of a charging diode 6 and a capacitor 5 is connected in parallel to the transistor 3, a driving current Is flowing to the coil 2 when the transistor 3 is closed and a charging current Ic flowing to the capacitor 5 from the coil 2 when the transistor 3 is opened flow through the current detection resistor 4. Therefore, the boosting power supply device 1 opens the transistor 3 when the driving current Is increases to a higher-side current threshold value iH and closes the transistor when the charging current Ic decreases to a lower-side current threshold value iL. In addition, when a power supply voltage or engine speed is reduced, the higher-side current threshold value iH decreases, and the lower-side current threshold value iL increases. Thereby, an increase range of the driving current Is is reduced so as to suppress an increase in temperature of the boosting power supply device. In this example, detection of an excitation current of the electromagnetic solenoid (electromagnetic coil) is not disclosed, but a current of the coil 2 which is a boosting inductive element and a boosted high voltage are detected, and both of the two are treated as input signals for an analog comparison circuit. Thus, a microcomputer 17 numerically records threshold values set for registers 28 and 29 or 54 and 55 (refer to FIG. 2 or FIG. 11) in threshold value changing circuits 15 and 51.